The biochemital determinants of alcoholism and genetic correlates for the variability in man's response to alcohol have remained obscure until recently. The identification of genetically determined isoenzymes of alcohol dehydrogenase with different catalytic properties may bear importantly upon this problem. New molecular forms of human liver alcohol dehydrogenase (ADH; alcohol:NAD+ Commun. 91, 1549Commun. 91, -1555. The distinguishing features of these specimens were (i) they showed activity optima for ethanol oxidation at both pH 7.0 and 10.0 and (ii) they formed electrophoretic-bands cathodic to the ,B isoenzyme. From such livers, three new ADH forms have now been iso a, one of which has a single pH optimum at 7.0 and two of which have dual optima at pH 7.0 and 10.0. These new forms were designated ADHlndianapolis forms 1,2, and 3, respectively. They can be differentiated from previously described ADH isoenzymes, including the so-called "atypical" isoenzyme, by their electrophoretic mobility, pH optima, and Km for ethanol (approxi-mately 60 mM at pH 7.5) Based upon the electrophoretic pattern of livers containing ADHirnii and the mobility of the three isolated molecular forms, ADAiLdianapolis may be the result of polymorphism at the ADH2 gene locus, which codes for the , subunit.Humans exhibit large individual differences in their rate of alcohol metabolism and in their physiological, psychological, and pathological response to ethanol consumption (1). The potential relationships between these phenomena and the remarkable variability and large number of alcohol dehydrogenase (ADH; alcohol:NAD+ oxidoreductase, EC 1.1.1.1) isoenzymes in human liver have been discussed (2). Such comparisons are of quite recent origin largely because a means for the isolation and characterization of the molecular properties of human ADH isoenzymes had not been available. Specific affinity chromatographic techniques for ADH isoenzyme purification (3, 4) and electrophoretic procedures capable of resolving hitherto unidentified molecular forms (5, 6) have improved the situation rapidly and significantly.A genetic modelt proposed some years ago (7) has thus far satisfactorily accounted for most variations in ADH isoenzymes observed in earlier studies. It did not encompass -r-ADH (2), however, which was discovered subsequent to the proposal of the model. Most recently, we discovered yet other ADH molecular forms in 16% of autopsy liver specimens from Indianapolis, IN (6), which also could not be classified according to that model. Characteristically these livers manifest two pH optima for ethanol oxidation at pH 7.0 and 10.0 and form electrophoretic bands cathodic to the f3,B isoenzyme (6).The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact. 5784We have now isolated three of these new molecular forms from such liver specimens. One of them exhibits a single activity o...